Camshaft 'slip'
 

Hi

I'm very slowly re conditioning a 1990 3TB...

I think this is obvious, but I'd like a second opinion before I rip into it....

I have the rocker cover off cleaning and replacing things, and now when I line it up for sealing (lobes down, I mark, piston at top) if I rotate it anti clockwise it feels like is jumps a gear on the timing chain on the bottom cog. When I check it, it's out of alignment again. If I rotate clockwise, no jumping.

It feels like a worn driven gear at the bottom of the cam chain (I don't know the proper name for the gear sorry) - surely it shouldn't jump a tooth no matter which direction you rotate?

Does it sound like an inspect and replace?

Opinions grateful...

Thanks
Jim

You shouldn't wind an engine backwards. Many varieties of cam chain tensioner only really work properly in one direction.

If when rotating in the correct direction you have NO slippage then I wouldn't be overly concerned just yet.

However, I wouldn't usually expect it to jump teeth rotating it by hand if everything is tensioned up properly but I've had it happen myself.

Have you checked the condition of the chain guides ?? A stretched cam chain will also slip more readily.

Have you got your tensioner installed correctly ?

Attachment 14818
That's a pic of a 2001 XT600E 4PT crankshaft camchain sprocket, which are really hard & don't appear to wear much, less than the camshaft sprocket anyway. Although you don't say what mileage your bike has done.
Looking at the chain side of the engine the normal direction of rotation of the crankshaft is anticlockwise.
Since you have the cam cover off I presume you have the camchain tensioner removed so it doesn't cause the camshaft to tilt in the cylinder head. So the chain is loose, right?
Because the camshaft is slightly forward of the crankshaft, the front section of the chain, if slack will want to fall away from the crankshaft sprocket, allowing it to jump a tooth when rotated.
Whereas the rear section of chain, if slack will want to fall onto the crankshaft sprocket i.e. not jump a tooth.
I hope this makes sense.
If you want to, you can inspect the crankshaft sprocket by looking down from the top with a torch.
To set up the cam timing, rotate the crankshaft anticlockwise slowly while applying light tension to the tensioner guide(rear guide) with a srewdriver through the tensioner hole(tensioner removed). Then install cam cover, then tensioner, in that order.

Bob

Sorry for the delayed response - working away for a week. Thanks for both responses they do help an awful lot -bob that does makes sense. It's kinda hard sometimes when you're entirely self taught...

Just to follow this up, I followed your instructions and lined it all up - no slippage, all looks good. Bike has done around 33k (km) according to odometer, but I'm pretty sure it was something of a farm bike for a while so it's anyone's guess.

Thanks again.